Author
Topic: problems with statpt in TS search (Read 7990 times)

We have a problem using stapt for determining the (a) transition state of the azaindole-water cluster. After running statpt the first time we have 4 negative eigenvalues in the stapt output. Running aoforce at the unchanged geometry shows only positive frequencies or sometimes a different number of negative frequencies at the same level of theory. If we start at this (unchanged) geometry a new optimization using jobex -trans, we often end up in a minimum along all modes.The same thing happens, if we elongate along one of the modes with negative frequency using the screwer tool.

Maybe this is due to the fact, that during optimization we cannot change the step size for the search algorithm. So we might just "pass" over the TS? Is there any way to adapt another step size especially concerning TS search?

Vacation is over so its time to answer some questions You probably used a Hessian update method within statpt. This results in only an approximateHessian matrix which can well have several negative eigenvalues, which most probablywill not be the same as calculated with analytical (aoforce) Hessian.Did you calculate Hessian with aoforce prior to running TS optimization? If nothing helpsyou can try to run statpt with analytical Hessian calculated every 3-5 steps. This will beexpensive but should lead finally to TS.The step size in statpt is adjusted automatically. You can only specify initial and maximumstep size (using define menu). Try to decrease the maximum step length, it may also help.